Strong photon-mixing of terahertz waves in semiconductor quantum wells induced by Rashba spin-orbit coupling.

We demonstrate that due to the Rashba spin-orbit coupling in semiconductor quantum wells, there is strong photo-mixing by mobile carriers in the terahertz frequency regime. The third order nonlinear current is of the same order of magnitude as the linear order current for an electric field intensity of 10(4) V cm(-1) at frequency around 1 THz, a situation easily achievable in a laboratory system. Unlike other nonlinear effects, the nonlinear current density due to the spin-orbit coupling is inversely proportional to the concentration of mobile carriers.